Various methods have been proposed in the past for the recovery of bitumen (sometimes referred to as “tar” or “bituminous material”) from oil sands as found in various locations throughout the world and in particular in Canada such as in the Athabasca district in Alberta and in the United States such as in the Utah oil sands. Typically, oil sand (also known as “bituminous sand” or “tar sand”) comprises a mixture of bitumen (in this context also known as “crude bitumen”, a semi-solid form of crude oil; also known as “extremely heavy crude oil”), sand, clay minerals and water. Usually, oil sand contains about 5 to 25 wt. % bitumen (as meant according to the present invention), about 1 to 13 wt. % water, the remainder being sand and clay minerals.
As an example, it has been proposed and practiced at commercial scale to recover the bitumen content from the oil sand by mixing the oil sand with water and separating the sand from the aqueous phase of the slurry formed. Disadvantages of such aqueous extraction processes are the need for extremely large quantities of process water (typically drawn from natural sources) and issues with removing the bitumen from the aqueous phase (whilst emulsions are being formed) and removing water from the bitumen-depleted sand.
Other methods have proposed non-aqueous extraction processes to reduce the need for large quantities of process water. Example of such a non-aqueous extraction process are disclosed in e.g. U.S. Pat. No. 3,475,318 and US2009/0301937, the teaching of which is hereby incorporated by reference.
U.S. Pat. No. 3,475,318 discloses a process of selectively removing bitumen from oil sands by solvent extraction with subsequent solvent recovery. The extraction solvent contains a saturated hydrocarbon having from 5 to 9 carbon atoms per molecule or mixtures thereof thereby leaving the asphaltenes on the sand. For removal of asphaltenes (to be used as process fuel), an aromatic solvent such as benzene or toluene is used.
US 2009/0301937 discloses a method for preparing solvent-dry, stackable tailings. The method includes a primary extracting process using a first solvent (typically a light aromatic solvent) that separates most of the bitumen from a material comprising bitumen and produces a first solvent-wet tailings. The first solvent-wet tailings are washed with a second solvent (typically an aliphatic solvent) that removes the first solvent from the tailings. The second solvent remaining in the tailings is removed thereby producing solvent-dry, stackable tailings.